[Show abstract][Hide abstract] ABSTRACT: This letter presents an experimental study that shows that a 3(rd) physical dimension may be used to further increase information packing density in magnetic storage devices. We demonstrate the feasibility of at least quadrupling the magnetic states of magnetic-based data storage devices by recording and reading information from nanopillars with three magnetically-decoupled layers. Magneto-optical Kerr effect microscopy and magnetic force microscopy analysis show that both continuous (thin film) and patterned triple-stack magnetic media can generate eight magnetically-stable states. This is in comparison to only two states in conventional magnetic recording. Our work further reveals that ferromagnetic interaction between magnetic layers can be reduced by combining Co/Pt and Co/Pd multilayers media. Finally, we are showing for the first time an MFM image of multilevel-3D bit patterned media with 8 discrete signal levels.
[Show abstract][Hide abstract] ABSTRACT: We present an experimental study on ultra-dense 3-D non-volatile magnetic universal logic gates with reconfigurable AND and OR functions. A four-layer magnetic structure with a net thickness of less than 30 nm is employed as a study illustration of a highly scalable magnetic logic device.
In the device, the magnetic state of the top output "soft" layer depends on the magnetic states of the remaining three "hard" layers used as two input and one reset layers, respectively. To build vertically oriented magnetic devices with a gradient of the coercivity and the magnetization across
the thickness, we use Co/Pd multilayers sputter-deposited via a combinatorial synthesis. Through a focused magneto-optical Kerr effect (F-MOKE) study, we relate input and output states in the 4-layer logic device to shoulders on major and minor M-H hysteresis loops. We use magnetic force microscopy
(MFM) to identify magnetic logic operations.
No preview · Article · Jun 2011 · Journal of Nanoelectronics and Optoelectronics
[Show abstract][Hide abstract] ABSTRACT: This letter addresses the fabrication and exploitation of ultrahigh coercivity magnetic force microscopy (MFM) probes to characterize high-magnetic moment nanostructures and devices. The L1<sub>0</sub> phase of FePt alloys together with CrRu and MgO seed layers are investigated as a method of increasing the coercivity of MFM probes to prevent their behavior as soft magnetic probes when used to image energized magnetic devices. The newly developed MFM probes, with coercivity higher than 11 kOe, are utilized to successfully analyze a modern perpendicular magnetic recording write head under various excitation conditions in order to perform writer saturation and remanence tests. The results include MFM micrographs of a fully energized magnetic writer, obtained with a probe-sample separation of only 10 nm.
Full-text · Article · Feb 2010 · IEEE Magnetics Letters
[Show abstract][Hide abstract] ABSTRACT: A cylindrical probe with almost perfectly flat plateaulike surface was focused ion beam (FIB) milled from an atomic force microscopy probe in order to create the required surface conditions for thin film deposition with finely controlled deposition/growth parameters. A composition of Pd(5 nm)/MgO(8 nm)/FePt(10 nm)/MgO(8 nm) was sputter deposited on the plateau probe, followed by deposition of a Pd (5 nm) protective layer. The plateau probe was then FIB-milled to produce a tip with a curvature radius of ∼25 nm . After annealing the probe at 650 ° C for ∼15 min to generate an ultrahigh anisotropy L1<sub>0</sub> phase, magnetic force microscopy (MFM) imaging was performed with the probe on magnetic tracks with linear densities ranging from 200 to 1200 KFCI. The results show sub-20-nm lateral resolution in ambient conditions and magnetic tracks, which are otherwise invisible to standard MFM probes, are clearly evident with the FIB-fabricated FePt probe. With relatively high spatial resolution and coercivity values higher than 1 T, among other applications, this type of probe may be ideal for high-quality MFM study of next-generation recording media.
No preview · Article · May 2009 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Today, conventional magnetic recording schemes are coming to an end because of the superparamagnetic limit. Heat-assisted magnetic recording (HAMR) may ultimately extend data densities beyond 1 TB/in<sup>2</sup>. HAMR systems utilize the phenomenon during which the magnetic properties of the recording media could be locally modified via heating (optionally, by an optical source in the near field) to temperature in the vicinity of the Curie value of the media material. As a result, heat induced by the optical source can temporarily reduce the magnetic coercivity of high anisotropy material to a level attainable by the magnetic writing head, thus making it feasible to record on relatively small ultra-high anisotropy (and thermally stable) grains, consequently enhancing the areal density dramatically. The key challenge is to develop a near-field transducer capable of delivering over 50 nW into a spot diameter of 30 nm. Traditional fiber schemes are barely capable of 0.1 nW. To resolve the issue, a laser diode could be placed with the emitting edge only a few nanometers away from the recording media. The light can propagate through a nanoaperture on the surface of an aluminum-coated emitting edge. This paper will present an experimental study of recording characteristics of various near-field transducers fabricated via focused ion beam (FIB). To count the number of photons emitted in the near field, a scanning near-field optical microscopy system has been implemented. The experiments indicate that the FIB-fabricated transducers could deliver power of over a few microwatt into a 30-nm spot (Fig. 7).
No preview · Article · Dec 2008 · IEEE Transactions on Magnetics
[Show abstract][Hide abstract] ABSTRACT: A detailed analysis to the problem of skew angle sensitivity in perpendicular magnetic recording is presented. A proposed analytical model is supported by numerical simulations with a commercial boundary element software program. According to the presented equivalent magnetic circuit model, a single pole recording head with a laminated composition involving two layers of different magnetic materials could be used to localize adequately strong magnetic field in the vicinity of the trailing edge of the recording head. It is shown that the recording field generated under each lamination layer is proportion to the relative magnetic permeability of the respective layer. Such localization of the magnetic flux results in substantially reduced skew angle sensitivity.
No preview · Article · Nov 2008 · Journal of Nanoelectronics and Optoelectronics
[Show abstract][Hide abstract] ABSTRACT: The letter reports experimental data to demonstrate magnetic force microscopy (MFM) with sub-10-nm resolution under ambient conditions. To achieve this record high resolution, multidomain states in a nanomagnetic probe were controlled. Two demagnetized (multidomain) FePt (45/55) films sputtered on a silicon probe and separated by an 8 nm thick MgO layer were further annealed at temperature of 650 °C to trigger the high-anisotropy L10 phase. A field of above 2 T was applied to drive the probes into a saturated “single-domain” state. The multidomain probes were equivalently compared with state-of-the-art conventional MFM probes via comparative imaging of benchmark magnetic recording disks.
No preview · Article · Nov 2008 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: The concept of optical protein-based memory has been of interest since the early 1970s. Yet, no commercially available protein-based memory devices exist. This review presents an analysis of the main challenges associated with the practical implementation of such devices. In addition, the discussion includes details on the potential of using the unparalleled properties of photochromic proteins by creating an optical data storage disk drive with unmatched features and, particularly, record-high data densities and rates.
[Show abstract][Hide abstract] ABSTRACT: A magnetic force microscopy based study on the formation of stripe domains in Permalloy ( Ni <sub>80</sub> Fe <sub>20</sub>) thin films is presented. Our results show that the critical thickness for stripe domain initiation depended on the sputtering rate, the substrate temperature, and the film thickness. Beyond the stripe domain formation, an increase of the period of a highly ordered array of stripe domains was evident with increasing film thickness. Thin films sputtered at room temperature with thickness variation between ∼80 and ∼350 nm exhibited square-root growth dependency on stripe domains periodicity from ∼150 to ∼380 nm , respectively. Above a certain thickness, the domain period decreased and the periodicity deteriorated with the array becoming more random, which is a strong indicator of relatively high structural perpendicular anisotropy. To illustrate, Permalloy sputtered at 100 ° C initially showed linear dependence in stripe domain periodicity growth up until ∼650 nm thick films. The magnetic stripe domain structure began breaking down for thicker Permalloy films. Our data also suggested that the perpendicular anisotropy responsible for the formation of stripe domains might have resulted from strain-caused magnetostriction and the thin-film microstructure shape effect.
No preview · Article · May 2008 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Continuous device downscaling, growing integration densities of the nanoscale electronics and development of alternative information processing paradigms, such as spintronics and quantum computing, call for drastic increase in the data storage capacity. In this paper we review our recent results for the design, fabrication and characterization of the near-field optical transducer for heat-assisted magnetic recording for beyond the 10-Tbit/in(2) densities. In order to record information, the heat-assisted magnetic recording system uses not only magnetic but also thermal energy. For this reason the recording media with the substantially higher anisotropy could be utilized to achieve the ultra-high recording densities. In this review, we provide details of the design of the near-field transducer capable of delivering over 50 I-LW power into a spot with the diameter of 30 nm. Heat-assisted magnetic recording and spin-based information processing require accurate thermal management of magnetic thin films. Here we report the results of our preliminary investigation of thermal transport in Pd/CoPd/Pd magnetic multilayers with the thickness of individual layers in the nanometer range.
Preview · Article · Mar 2008 · Journal of Nanoelectronics and Optoelectronics
[Show abstract][Hide abstract] ABSTRACT: The paper outlines a review of multilevel (ML) and three-dimensional (3D) magnetic recording—a nanomagnetic recording technology suitable for information storage densities above 100 terabit/in2. To comply with the multilevel signal configuration, ML magnetic recording exploits a 3D head/media system powered with next-generation data coding methods. It is believed that combined with novel information processing techniques, relatively cost-effective ML systems could be scaled down to a single-grain spin level thus enabling memory with effective areal densities above 100 Terabit/in2.
Full-text · Article · Nov 2007 · Journal of Nanoelectronics and Optoelectronics
[Show abstract][Hide abstract] ABSTRACT: A focused ion beam (FIB) fabricated nanolaser is demonstrated to be able to focus light with power of over 250 nW into a 30 nm spot. To fabricate a nanolaser, a 100 nm thick aluminum film was deposited on the emitting edge of a diode laser. FIB was used to etch various apertures into the film. The power was measured by a scanning near-field optical microscope in the near-field regime with a 10 nm separation between the probe and the air bearing surface of the nanolaser. Out of four different shapes under study, “C”-shape aperture was found to have the highest throughput.
No preview · Article · Oct 2007 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: The communication illustrates how focused ion beam-modified nanomagnetic probes could be used to image patterned media with the resolution of a few nanometers only and thus suitable for densities above 10 terabit/in2. To take advantage of the modified probes, the measured signal is deconvolved with the sensitivity field inherent to the probe. Focused ion beam is used to trim silicon probes into the probes with the adequate geometry to satisfy the requirements on the sensitivity field. The measurements indicate that the resolution of magnetic force microscopy could be made comparable with the resolution of atomic force microscopy.
No preview · Article · Jul 2007 · Journal of Nanoelectronics and Optoelectronics
[Show abstract][Hide abstract] ABSTRACT: In this paper, it is argued that perpendicular recording in the most popular current form--with the use of a continuous soft underlayer (SUL)--may not be the most optimal way to maximize the achievable areal density. As a possible solution, patterning of SUL is discussed. The purpose of patterning of a SUL is to effectively move the image head closer to the recording media, as compared to the real recording head, and thus increase the net recording field and the field gradient across the thickness of the media. Various patterning configurations and combinations with recording layers are comparatively studied. It is illustrated that with a patterned SUL, the recording and sensitivity fields, responsible for writing and reading information, respectively, could be not only increased by several factors but also localized across the entire thickness of the recording media.
Full-text · Article · Feb 2007 · Journal of Nanoscience and Nanotechnology
[Show abstract][Hide abstract] ABSTRACT: Perpendicular recording may be the most viable, near future, replacement for the longitudinal core technology in ultrahigh-density magnetic disk storage. Central to this mode of recording is a soft underlayer (SUL) which facilitates flux flow between writer poles, and is responsible for an effective increase in recording field. However, there are controversies concerning the effectiveness and limitations of using soft underlayers; among which are readback noise and inadequate switching torque. Patterned SUL is proposed as a new and viable approach to SUL limitations in perpendicular media, with improved system performance. Numerical models have been developed using commercially available FEM and BEM software suites (ANSYS and Ampere) to demonstrate key advantages of patterned SUL in perpendicular media
No preview · Article · Nov 2006 · IEEE Transactions on Magnetics